The present invention relates to a locking device for locking an output shaft when the machine has no torque output while an external force is applied to the output shaft.
Conventional electric machines, such as electric drills, screwdrivers, lathe and millers, comprise an output shaft coupled to a driving device that transfers power to the output shaft. A tool is mounted to the output shaft for being driven thereby. A clutch device is usually arranged between the output shaft and the driving device for selectively coupling the output shaft to the driving device to transfer the power of the driving device to the output shaft. On the contrary, when the clutch device disengages, the power from the driving device cannot be transferred to the output shaft. To remove the tool from the output shaft, a chuck or similar device must be employed to lock the output shaft. In other words, an operator has to operate an additional chuck to hold the output shaft. In case that the output shaft is not locked, the driving device may get damaged by an external force applied to the output shaft, which is transferred through the clutch device, if the clutch device is not set at a disengagement position.
The present invention intends to provide an output shaft locking device that locks the output shaft to prevent an external force applied thereto from being transferred to the driving device without the application of a chuck.
In accordance with one aspect of the present invention, there is provided an output shaft locking device which comprises a hollow frame having an output shaft extending therethrough wherein the output shaft has a polygonal end for coupling to a driving device.
A locking device comprises a fixed ring mounted to an underside of the hollow frame. An inner ring is rotatably received in the fixed ring. A first polygonal hole is defined through the inner ring and recesses are defined in an underside of the inner ring.
The driving device has a driving disk. A second polygonal hole is defined through the driving disk. A plurality of protrusions is formed on one end of the driving disk and matches with the recesses in the underside of the inner ring. The polygonal end of the output shaft engages with the first polygonal hole and the second polygonal hole. Gaps are respectively defined between two sides of each of the protrusions of the driving disk and the recesses in the inner ring, and defined between the two sides of the polygonal end of the output shaft and the first polygonal hole in the inner ring. Two gaps are respectively defined between two sides of the polygonal end of the output shaft and the second polygonal hole in the driving disk. The output shaft is locked when the driving disk is not rotated by the locking device, which allows an operator to remove a tool that is coupled to the output shaft without fixing the output shaft with a chuck.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.
FIG. 1 is an exploded view showing a locking device, an output shaft and a driving disk of an electric machine tool in accordance with the present invention;
FIG. 2 is a cross-sectional view showing an assembly of the locking device, the output shaft and the driving disk of the present invention;
FIG. 3 is a plan view of the locking device of the present invention;
FIG. 4 shows a polygonal end of the output shaft engaging a polygonal hole defined in the inner ring;
FIG. 5 shows angles between two sides of the polygonal end of the output shaft and the polygonal hole in the driving disk;
FIG. 6 shows angles xcex11 and xcex12 between two sides of each protrusion of the driving disk and the corresponding recess defined in the inner ring, and angles xcex21 and xcex22 respectively defined between two sides of the polygonal end of the output shaft and the first polygonal hole in the inner ring;
FIGS. 7a and 7b show the locking device and the output shaft when the driving disk outputs power, and
FIGS. 8a and 8b show the locking device and the output shaft that is subject to a reaction torque.